Gen 3 Transmission Life?

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PostPosted: Fri Apr 01, 2016 11:38 am
What you will want to monitor are clutches. It seems to be the weak point in the system and so far I've seen three distinct failures. The clutch disk is solid (no springs). I don't know if this is a contribution to transmission failures as well (I've lost both 2nd and 3rd gears).

1) Cracking of the clutch disk. Had this experience personally when doing a transmission change (I'll wait to comment until I see how long the current rebuild lasts!)

2) Failure of the clutch material bonding. Seen this happen to at least one local driver and feedback from others

3) Shearing of the spline on the clutch disk (better than shearing the transmission shaft, though)

I'm also seeing an increasing failure rate on CV joints, especially the outer left.

You may want to consider the clutch an annual maintenance item and certainly look at it carefully whenever you have the transmission out of the car. Careful shifting may help as well.
Bob Breton - SRF 51 - San Francisco Region

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PostPosted: Sat Apr 02, 2016 8:03 pm
breton wrote:You may want to consider the clutch an annual maintenance item


How many races do you run in a typical year. I run 5 or 6 weekends. I hope not to need to pull the engine every winter.
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PostPosted: Sun Apr 03, 2016 2:28 pm
I have about 80 hours on the motor since conversion last year. Typically run a 14 race / 7 weekend schedule, plus 3 Majors last year. More hours than usual to-date due to a lot more than the usual number of test days (generally ran one before each weekend when possible last year) with 4-5 test/track days this year to get time on the tires.

If you're running a test day along with 5-6 weekends (assuming they're all doubles) I assume that's in the range of 4+ hours per weekend that could run 20-24+ hours a season, so perhaps every other season would be OK, but frankly I'd advise a teardown in the winter if you have the time.

We may have a clutch "fix" in the works so you either wait until a failure of fix it when new parts become available. BTW, the cost of that clutch disk will make your eyeballs bulgt :shock:
Bob Breton - SRF 51 - San Francisco Region

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PostPosted: Sun Apr 03, 2016 10:06 pm
breton wrote:I have about 80 hours on the motor since conversion last year. Typically run a 14 race / 7 weekend schedule, plus 3 Majors last year. More hours than usual to-date due to a lot more than the usual number of test days (generally ran one before each weekend when possible last year) with 4-5 test/track days this year to get time on the tires.

If you're running a test day along with 5-6 weekends (assuming they're all doubles) I assume that's in the range of 4+ hours per weekend that could run 20-24+ hours a season, so perhaps every other season would be OK, but frankly I'd advise a teardown in the winter if you have the time.

We may have a clutch "fix" in the works so you either wait until a failure of fix it when new parts become available. BTW, the cost of that clutch disk will make your eyeballs bulgt :shock:


Thanks. I learned way back in kart racing that you keep costs down by minimizing failures not by maximizing part life. But I still like to get an idea when someone is doing maintenance once a year, how many hours a year is for them. I suspect at the end of this year it will come back out even though it will only have 4 weekends on it.

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PostPosted: Tue Sep 10, 2019 2:16 pm
Last time this post was active was 2016 so I thought I'd resurrect it.

Now that there is a much larger sample size (both in number of Gen3's and the hours of track time) in the last 3 years, what are people seeing for tranny life? I ask because just this past weekend at BHF there were two tranny failures. I'm hearing folks are getting as few as 4 weekends and as many as 12 weekends before failure. Some are going back to the "rounded" gears, Mazda gears, etc.

-What is failing?
-How long have you been running your tranny?
-What gears are you running?

I have 8 weekends on mine (it's working perfectly right now) but I'm sending it back for a refresh this winter. I'll publish a full report on wear, etc. when it comes back.

Ron
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PostPosted: Wed Sep 11, 2019 9:52 pm
Back to the Mazda gears on my latest rebuild this year after experiencing a failure of the straight cut gears on my last rebuild. The straight cut gears appear to have not been hardened correctly, so there is noticeable deterioration on the gear surfaces, leading to failure. Given the number of drivers who have experienced similar failures and have gone back to Mazda gears, this does not appears to be a unique situation. In this case, you don't get what you pay for. I'm getting, at best, 1-2 seasons on the transmission. Primary failures are 3rd gear.

I would say an annual rebuild is pretty much standard, pretty much around the same failure/wear points of the clutches. I just put in the "new/new" clutch and was very disappointed to suddenly have the car develop a massive slip in 2nd gear through the shift into 3rd in it's second race weekend. I thought it might be a complete failure but after "babying" the clutch for several laps (e.g. very slow shifts, avoiding 2nd gear, running a second a lap slower) the engagement seemed to return to normal. I suspect it was a release issue where the clutch was slow to engage after a shift, resulting in slippage and overheating. Not too confident it will last another weekend, but since there's only one more race in the season I'll give it a try to see if it's salvageable. If I recall correctly this is clutch #5 or 6 since the conversion (at least 2 with cracked plates, 2 or 3 with stripped splines, and now the "new-new" slippage). Pretty much anytime we pull the engine we're replacing the clutch.
Bob Breton - SRF 51 - San Francisco Region
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PostPosted: Thu Sep 12, 2019 12:57 am
We have a large number of cars/hours running GEN3's. In the early days, we had problems with the GEN3 transaxles but that has changed. In the past, we were using oil that caused issues with the synchros but after changing oil we haven't had a single issue with shifting. With changes to a special oil, changing rebuilding techniques, regular service, and new clutches we are now getting great life with transaxles. I have two rebuilt transaxles that have been in the trailer for months.

Over the last year or so, we have run GEN3's a total of about 240 hours with only 3 transaxle issues. So as of now, we are getting at least 80 hours of life before rebuild.

In regards to the clutch issue. The new-sprung clutch reduces the stress put on the transaxle and drivetrain. Installing the new-sprung clutch isn't just plug and play and we recommend special setup procedures. See either the section on the sprung clutch in this forum. When installed correctly, the new-sprung clutch works great and will result in longer clutch disk and driveline life.

An example of the splines damaged by the direct coupling and pulsing in the rotation of the motor is below. The 4 cylinder motor only fires twice per revolution and that results in pulsing and not pure smooth rotation. The pulsing puts a large harmonic load on the drive train that induces failures. If the splines on the fixed disk clutch are getting damaged then you know the gears are getting stressed.
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Clutch Disk Failure L.jpg
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PostPosted: Thu Sep 12, 2019 7:19 am
brichardson wrote:We have a large number of cars/hours running GEN3's. In the early days, we had problems with the GEN3 transaxles but that has changed. In the past, we were using oil that caused issues with the synchros but after changing oil we haven't had a single issue with shifting. With changes to a special oil, changing rebuilding techniques, regular service, and new clutches we are now getting great life with transaxles. I have two rebuilt transaxles that have been in the trailer for months.

Over the last year or so, we have run GEN3's a total of about 240 hours with only 3 transaxle issues. So as of now, we are getting at least 80 hours of life before rebuild.



Care to tell us what oil you are using?
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PostPosted: Thu Sep 12, 2019 11:59 pm
I will tell you what not to use for oil, 75/95 synthetic that is GL-5. GL-5 is great for differentials but not synchros. The super slick formula is so slick makes the synchro rings slip rather than grab onto the cone to slow/match the gears. We don't recommend using any GL-5 gear oil. Use oil designed for use with synchrosmesh transmissions. Take a look at the Lucus product, it isn't designed for synchrosmesh transmissions but differentials. https://lucasoil.com/pdf/TDS_Lucas-Synt ... 75W-90.pdf
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PostPosted: Fri Sep 13, 2019 10:51 am
Based on other recommendations, I switched from using RedLine D4 ATF (note this is NOT a GL-5 rated, so it should be OK) to RedLine MT-90 in my most recent rebuilt. I've noticed it's quite a bit "thinner" than the D4, but was recommended by a reliable source as a better fit for these transmissions. You're "mileage" may vary (hopefully mine, as well!)
Bob Breton - SRF 51 - San Francisco Region
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